batteries - Solar panel lipo and usb

I connect a 5v 5w solar panel a usb port and a 3.7v 2.5A lipo with pcb. If I connect a phone to usb port it doesn't charge, but if I remove the battery from the circuit, it does. I suppose it's because battery pcb downgrade the voltage to 4.2v or there is not enough energy to serve both. There is a simple way to prioritize the usb or make them share? Thanks in advance for your help

PS Sorry to eventual mistakes but I'm still learning electronics. I did not blow anything yet, thanks also to t

______________________________________

Summary of requirement:

Given:

• 5V 5 Watt PV panel


• Cellphone with "USB" "5V" charger input.


• Single cell LiPo 3.7V nominal 2500 mAh.

Requirement:

• Use PV to charge phone if connected.


• Otherwise charge battery.


• If possible share PV energy between phone and battery if both present.

Problem:

Connecting the panel to the LiPo loads it to battery voltage which is too low a V to operate the phone charging circuit.